In a logical overlay network, each gateway provides connectivity to its local workloads for them to communicate with other remote workloads connected to remote gateways. This connectivity includes both L2 and L3 traffic. Through the data plane of the logical network, a gateway typically learns the media access control (MAC) addresses for all workloads connected to it via L2 switches and may also learn the IP/MAC bindings associated with those workloads. Furthermore, a gateway will learn the remote workload MAC addresses connected via remote gateways. To provide redundancy, a workload may be multi-homed to more than one gateway. One gateway acts as an active gateway while another gateway backs up that active gateway in a standby capacity. Network, traffic from a workload will flow through the active gateway as long as the active gateway remains active. However, when the active gateway fails, or is otherwise unable to continue handling traffic, the traffic will flow via the backup gateway.
An issue with data plane MAC address learning in the active/backup relationship described above is that remote gateways need to relearn the MACs addresses via the newly activated backup gateway. That relearning process will rely on MAC address relearning due to bi-directional traffic or, as a last resort, aging out of MAC addresses in the absence of frames from the sources. The process can, therefore, lead to a larger convergence time for the MAC addresses to be relearned as being associated with the backup gateway. Even if the MAC addresses can be re-learned via a central control plane, rather than the data plane, the time it takes the control plane to learn about the switchover to the newly active gateway, or to re-teach the remote gateways about the MAC addresses' new association with the backup gateway can still lead to higher convergence time.